LACTATION 605 



was greath 7 increased, but the evening milk was reduced almost in 

 proportion.) The ratio of nitrogen to lactose in the milk was almost 

 constant throughout. 



As a result of withholding food for a few days, together with an 

 injection of phloridzin, thereby considerably reducing the nutrition, 

 the yield of milk could be greatly diminished but the fat percentage 

 rose. The fat, however, subsequently diminished, possibly as a 

 secondary effect of the decreased secretion by the gland-cells. On 

 feeding such animals the milk yield rapidly increased, but the 

 percentage of fat decreased. Hammond found also that the amount 

 of milk produced by the action of pituitary extract varied with the 

 state of nutrition, and he concludes that the fat percentage of the 

 pituitary milk is increased by a condition of lowered nutrition in 

 the same way as with normal milk. Further, after injecting 

 adrenalin the fat percentage in the milk is increased but the actual 

 quantity of milk is somewhat below the normal. 



Taylor and Husband, 1 as a result of a recent investigation upon 

 cow's milk, have reached the following conclusions : The percentage 

 composition of the milk seems to be determined by its rate of 

 secretion. The percentages of protein and ash, as well as of fat, vary 

 inversely, and the percentage of lactose varies directly, as the daily 

 volume, the greatest variation being shown by the fat and the least 

 by the inorganic elements. There is an inverse relationship between 

 the percentage of lactose and the percentages of all the other con- 

 stituents of the milk, this being particularly apparent in the case 

 of the fat. Diet has no direct influence on the percentage composi- 

 tion of the milk, except in the case of the non-protein nitrogen 

 which is not a product of the mammary gland. Diet has, however, 

 an indirect influence by reason of its effect on the daily volume. A 

 high protein diet would appear to stimulate the rate of secretion of 

 the milk. It is suggested, further, that the quantity of lactose 

 elaborated by the gland may control the daily volume of milk, 

 and that therefore the rate of its elaboration is a regulative factor 

 in the rate of milk secretion. 



THE NORMAL GROWTH OF THE MAMMARY GLANDS 



The growth of the mammary glands in the rabbit has been 

 described by Miss Lane-Claypon and Starling, from whose paper the 

 following account is taken. 2 



1 Taylor and Husband, "The Effect on the Percentage Composition of 

 the Milk of (a) Variations in the Daily Volume, and (b) Variations in the 

 Nature of the Diet," Jour, of Agric. Science, vol. xii., 1922. This paper contains 

 further references. 



2 Lane-Claypon and Starling, " An Experimental Inquiry into the Factors 

 which Determine the Growth and Activity of the Mammary Glands," Proc. 

 Roy. Soc., B., vol. Ixxvii., 1906. See also Brouha, loc. tit. 



